Showing 1–50 of 403 results for author: Zhang, J

Two birds with one stone: simultaneous realization of both Lunar Coordinate Time and lunar geoid time by a single orbital clock

Authors: Tian-Ning Yang, Ren-Fang Geng, Jing Zhang, Chong Yang, Yong Huang, Yi Xie

Abstract: Context. Among options for definition of the lunar reference time, the option taking Lunar Coordinate Time (O1) has its simplicity but cannot be realized by any clock without steering, while another option adopting the lunar geoid (selenoid) proper time (O2) has its convenience for users on the lunar surface but would bring a new scaling of spatial coordinates and mass parameter of the Moon. Aims.… ▽ More Context. Among options for definition of the lunar reference time, the option taking Lunar Coordinate Time (O1) has its simplicity but cannot be realized by any clock without steering, while another option adopting the lunar geoid (selenoid) proper time (O2) has its convenience for users on the lunar surface but would bring a new scaling of spatial coordinates and mass parameter of the Moon. Aims. We propose a ''time aligned orbit'' that the readings of an ideal clock in this orbit could equal to the selenoid proper time in O2 and these readings could be converted to Lunar Coordinate Time in O1 by a known linear transformation. Methods. We show that there exist the time aligned orbit around the Moon with its semi-major axis of about 1.5 lunar radius slightly depending on its inclination. We conduct a set of numerical simulations to assess to what extent a clock on these orbits could realize O2 in a more realistic lunar environment. Results. We find that the proper time in our simulations would desynchronize from the selenoid proper time up to 190 ns after a year with a frequency offset of 6E-15, which is solely 3.75% of the frequency difference in O2 caused by the lunar surface topography. These numbers might be further reduced to 13 ns and 4E-16, if we could account for the deviation of the mean orbits in our simulations from the nominal ones. Conclusions. One might simultaneously realize O1 and O2 by deployment of a single clock in the time aligned orbit. This approach also has its scalability for other terrestrial planets beyond the Earth-Moon system. △ Less

Submitted 28 December, 2025; originally announced December 2025.

Numerical simulation of lunar response to gravitational waves and its 3D topographic effect using the spectral-element method

Authors: Lei Zhang, Han Yan, Jinhai Zhang, Xian Chen

Abstract: The Moon has been regarded as a natural Weber bar capable of amplifying gravitational waves (GWs) for detecting events across a wide range of frequencies. However, accurately determining the amplification effects remains challenging due to the absence of 3D numerical simulation methods. In this study, we develop a high-order 3D finite element method (spectral-element method, SEM) to numerically si… ▽ More The Moon has been regarded as a natural Weber bar capable of amplifying gravitational waves (GWs) for detecting events across a wide range of frequencies. However, accurately determining the amplification effects remains challenging due to the absence of 3D numerical simulation methods. In this study, we develop a high-order 3D finite element method (spectral-element method, SEM) to numerically simulate the lunar response to GWs below 20 mHz. We verify the accuracy of our method by comparing the resonant peaks of our results with those from semi-analytical solutions and find that the frequency deviation is less than 3% for the first peak at about 1 mHz and less than 0.8% for the subsequent peaks up to 10 mHz. Using this method, we evaluate the amplification of GW signals due to 3D topographic effects of the Moon, and we find enhancements at a series of specific frequency components. These results highlight the non-negligible effect of surface topography on the lunar response to GWs, as a fundamental factor that holds significant implications across both global and regional analyses. Our work paves the way for a comprehensive evaluation of the Moon's resonant response to GWs, helpful for the strategic planning of lunar GW detections. △ Less

Submitted 25 December, 2025; originally announced December 2025.

Comments: Accepted for publication in Physical Review D

Synthesis of a high intensity, superthermal muonium beam for gravity and laser spectroscopy experiments

Authors: Jesse Zhang, Aldo Antognini, Marek Bartkowiak, Klaus Kirch, Andreas Knecht, Damian Goeldi, David Taqqu, Robert Waddy, Frederik Wauters, Paul Wegmann, Anna Soter

Abstract: The universality of free fall, a cornerstone of Einstein's theory of gravity, has so far only been tested with neutral composite states of first-generation Standard Model (SM) particles, such as atoms or neutrons, and, most recently, antihydrogen. Extending these gravitational measurements to other sectors of the SM requires the formation of neutral bound states using higher-generation, unstable p… ▽ More The universality of free fall, a cornerstone of Einstein's theory of gravity, has so far only been tested with neutral composite states of first-generation Standard Model (SM) particles, such as atoms or neutrons, and, most recently, antihydrogen. Extending these gravitational measurements to other sectors of the SM requires the formation of neutral bound states using higher-generation, unstable particles. Muonium, the bound state of an antimuon ($μ^+$) and an electron ($e^-$), offers the possibility to probe gravity with second-generation (anti)leptons, in the absence of the strong interaction. However, the short $μ^+$ lifetime ($τ_μ\approx 2.2~μ$s) and the existing diffuse thermal muonium sources rendered such measurements unfeasible. Here, we report the synthesis of a high-brightness muonium beam, extracted from a thin layer of superfluid helium by exploiting its chemical potential and unique transport properties. The mean longitudinal velocity (${v}\approx 2180~\rm{m/s}$) and narrow distribution (${Δv}< 150 ~\rm{m/s}$) of the atoms characterise a superthermal beam, while yields are similar to the highest intensity diffuse sources. This new beam is expected to enable muonium interferometry and a percent-level measurement of its gravitational acceleration, providing the first direct test of the Weak Equivalence Principle with second-generation (anti)matter. Its unprecedented brightness also opens the way to sub-kHz 1S-2S spectroscopy, enabling precise determination of the muon mass and stringent tests of bound-state quantum electrodynamics. △ Less

Submitted 22 December, 2025; originally announced December 2025.

A Universal Geometric Framework for Black Hole Phase Transitions: From Multivaluedness to Classification

Authors: Shi-Hao Zhang, Zi-Yuan Li, Jing-Fei Zhang, Xin Zhang

Abstract: Recent studies have revealed synchronized multivalued behavior in thermodynamic, dynamical, and geometric quantities during the black hole first-order phase transition, which enables a diagnosis from different perspectives, yet its fundamental origin has remained poorly understood. By constructing a unified geometric framework integrating real analysis and covering space theory, we reveal the univ… ▽ More Recent studies have revealed synchronized multivalued behavior in thermodynamic, dynamical, and geometric quantities during the black hole first-order phase transition, which enables a diagnosis from different perspectives, yet its fundamental origin has remained poorly understood. By constructing a unified geometric framework integrating real analysis and covering space theory, we reveal the universal mathematical mechanism behind this phenomenon. We prove that this multivaluedness originates from two non-degenerate critical points in the temperature function $T(r_+)$, where $r_+$ is the horizon radius, which fold the parameter space into a three-sheeted covering structure. As a direct application, we propose that a black hole undergoes a first-order phase transition if and only if its $T(r_+)$ curve has two extrema. Accordingly, we establish a classification scheme, denoted $A1$, $A2$, and $B$ for black holes. This scheme offers a complementary perspective to classifications based on global topological invariants. Our work provides a theoretical foundation for diagnosing phase transitions via multivaluedness and establishes a unified geometric perspective on black hole thermodynamics, chaotic dynamics, and spacetime structure during first-order phase transitions. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: 8 pages, 2 figures

Efficient pulsar distance measurement with multiple nanohertz gravitational-wave sources

Authors: Si-Ren Xiao, Ji-Yu Song, Yue Shao, Ling-Feng Wang, Jing-Fei Zhang, Xin Zhang

Abstract: In recent years, pulsar timing arrays (PTAs) have reported evidence for a nanohertz gravitational-wave (GW) background. As radio telescope sensitivity improves, PTAs are also expected to detect continuous gravitational waves from individual supermassive black hole binaries. Nanohertz GWs generate both Earth and pulsar terms in the timing data, and the time delay between the two terms encodes the p… ▽ More In recent years, pulsar timing arrays (PTAs) have reported evidence for a nanohertz gravitational-wave (GW) background. As radio telescope sensitivity improves, PTAs are also expected to detect continuous gravitational waves from individual supermassive black hole binaries. Nanohertz GWs generate both Earth and pulsar terms in the timing data, and the time delay between the two terms encodes the pulsar distance. Precise pulsar distance measurements are critical to fully exploiting pulsar-term information, which can improve the measurement precision of GW sources' sky position parameters and thus enhance the GW sky-localization capability. In this work, we propose a new pulsar distance estimation method by using pulsar-term phase information from GWs. We construct two-dimensional distance posteriors for pulsar pairs based on the simulated GW signals and combine them to constrain individual pulsar distances. Compared with the existing one-dimensional method, our approach reduces the impact of source-parameter uncertainties on pulsar distance measurements. Considering four GW sources and a PTA of 20 pulsars with a white-noise level of 20 ns, we find that a significant fraction of pulsars at distances $\lesssim 1.4$ kpc can achieve sub-parsec distance precision over a 15-year observation. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: 13 pages, 4 figures

Constraints on Reversing the Thermodynamic Arrow of Time from Black Hole Thermodynamics, Wormholes, and Time-Symmetric Quantum Mechanics

Authors: Kevin Song, John Zhang

Abstract: Can the thermodynamic arrow of time in a single universe be reversed, even temporarily, within semiclassical gravity without invoking additional universes or branches? We address this question in a single, connected spacetime where quantum field theory is coupled to classical general relativity, and where black holes, traversable wormholes, and time-symmetric or retrocausal formulations of quantum… ▽ More Can the thermodynamic arrow of time in a single universe be reversed, even temporarily, within semiclassical gravity without invoking additional universes or branches? We address this question in a single, connected spacetime where quantum field theory is coupled to classical general relativity, and where black holes, traversable wormholes, and time-symmetric or retrocausal formulations of quantum mechanics might naively appear to open channels for entropy export or cancellation. After distinguishing fine-grained, coarse-grained, and generalized gravitational entropy, and formulating a cosmological coarse-grained entropy, we treat black hole evaporation, wormholes constrained by quantum energy inequalities, and two-time boundary-value frameworks (including absorber-type and two-state-vector formalisms) within a common information-theoretic language. We then introduce a "Global Entropy Transport" (GET) framework and derive a sectoral inequality that bounds the net decrease of matter-plus-radiation entropy in terms of changes in horizon area and correlation (mutual-information) terms, assuming the generalized second law and modern focusing and energy conditions. Within this framework, black holes, wormholes, and retrocausal protocols can at most redistribute entropy among matter, radiation, and gravitational sectors and reshape the local pattern of entropy production. They do not, under current semiclassical, holographic, and statistical-mechanical constraints, permit a genuine reversal of the universal thermodynamic arrow in a single connected universe. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Comments: 22 pages

Images of shadow and thin accretion disk around Bardeen black hole surrounded by perfect fluid dark matter

Authors: Haiyuan Feng, Ziqiang Cai, Hao-Peng Yan, Rong-Jia Yang, Jinjun Zhang

Abstract: We investigated the shadow and optical appearance of Bardeen black hole (BH) immersed in perfect-fluid dark matter (PFDM). Using the EHT data, we find that the DM parameter is restricted to a narrow allowed range, confined to values of $\mathcal{O}(10^{-1}-10^{-2})$. Additionally, we observed that increasing the DM parameter substantially enlarges the photon sphere, the critical impact parameter,… ▽ More We investigated the shadow and optical appearance of Bardeen black hole (BH) immersed in perfect-fluid dark matter (PFDM). Using the EHT data, we find that the DM parameter is restricted to a narrow allowed range, confined to values of $\mathcal{O}(10^{-1}-10^{-2})$. Additionally, we observed that increasing the DM parameter substantially enlarges the photon sphere, the critical impact parameter, and thus the shadow radius, whereas the magnetic charge $g$ produces only negligible corrections. The DM component also modifies the optical appearance of the accretion disk: higher $b$ systematically suppresses the observed radiation intensity and reduces image brightness, while changes in $g$ yield only marginal effects. Subsequently, using the Novikov-Thorne thin disk model, we analyze primary and secondary images, observed flux, and redshift patterns, showing that PFDM noticeably alters image size and brightness whereas magnetic charge has a negligible influence. No blueshifted regions appear in any configuration. These results highlight several promising observational signatures for testing DM environments and nonlinear electrodynamic effects around BHs. △ Less

Submitted 30 November, 2025; originally announced December 2025.

Comments: 44 pages, 86 figures

Robust evidence for dynamical dark energy in light of DESI DR2 and joint ACT, SPT, and Planck data

Authors: Tian-Nuo Li, Guo-Hong Du, Sheng-Han Zhou, Yun-He Li, Jing-Fei Zhang, Xin Zhang

Abstract: Recent baryon acoustic oscillation (BAO) measurements released by DESI, when combined with cosmic microwave background (CMB) data and type Ia supernova (SN) data, suggest a significant preference for dynamical dark energy (DDE) that exhibits the phantom-like behavior in the past and has transitioned into quintessence-like behavior today. In this work, we conduct a comprehensive analysis of six rep… ▽ More Recent baryon acoustic oscillation (BAO) measurements released by DESI, when combined with cosmic microwave background (CMB) data and type Ia supernova (SN) data, suggest a significant preference for dynamical dark energy (DDE) that exhibits the phantom-like behavior in the past and has transitioned into quintessence-like behavior today. In this work, we conduct a comprehensive analysis of six representative DDE parametrization models by utilizing the latest and most precise CMB data jointly from ACT, SPT, and Planck, in conjunction with BAO data from DESI DR2 and SN data from DESY5, PantheonPlus, and Union3. Our overall analysis indicates that the preference for DDE in the Quintom-B regime remains robust, regardless of the DDE parameterization model and the data combination employed. The trend of this preference is significantly strengthened with the support of DESY5 SN data. Specifically, when using the CMB+DESI+DESY5 data, for the Barboza-Alcaniz (BA) model, we obtain $w_0 = -0.785 \pm 0.047$ and $w_a = -0.43^{+0.10}_{-0.09}$, which significantly deviate from the $Λ$CDM values and provide evidence for DDE at the $4.2σ$ level. By the reconstruction of the dark energy equation of state $w(z)$, normalized dark energy density $f_{\mathrm{DE}}(z)$, and the deceleration parameter $q(z)$, we also observe clear departures from $Λ$CDM, further reinforcing the case for DDE. Furthermore, the Bayesian evidence analysis indicates that the Chevallier-Polarski-Linder, BA and Exponential models are moderately favored relative to $Λ$CDM based on the CMB+DESI+DESY5 data. △ Less

Submitted 27 November, 2025; originally announced November 2025.

Comments: 13 pages, 4 figures

Universal scalarization in topological AdS black holes

Authors: Zi-Qiang Zhao, Zhang-Yu Nie, Shao-Wen Wei, Jing-Fei Zhang, Xin Zhang

Abstract: We investigate the universal behavior of black hole scalarization induced by a charged scalar field in the extended phase space of the asymptotic AdS spacetime with three distinct horizon topologies. The results indicate that in all the three cases, the charged black hole spacetime undergoes scalarization at low temperatures. Notably, the spherical topology is unique in that its domain of scalariz… ▽ More We investigate the universal behavior of black hole scalarization induced by a charged scalar field in the extended phase space of the asymptotic AdS spacetime with three distinct horizon topologies. The results indicate that in all the three cases, the charged black hole spacetime undergoes scalarization at low temperatures. Notably, the spherical topology is unique in that its domain of scalarization theoretically extends to much higher temperatures under low pressure in the extended phase space. Moreover, the scalarization process in the spherical case exhibits complex phase transition behaviors without additional non-linear terms, which are similar to those in the planar and hyperbolic topologies with the assistance of non-linear terms. With increasing pressure in the extended phase space, the condensate of the scalarization in all three cases undergoes a transition from the first-order style to a cave-of-wind style. This study provides deeper insight into the zeroth-order phase transition during black hole scalarization and reveals the complete phase structure of black holes in the extended phase space. △ Less

Submitted 22 November, 2025; originally announced November 2025.

Comments: 5 pages, 3 figures

Detectability of axion-like dark matter for different time-delay interferometry combinations in space-based gravitational wave detectors

Authors: Yong-Yong Liu, Jing-Rui Zhang, Ming-Hui Du, He-Shan Liu, Peng Xu, Yun-Long Zhang

Abstract: In the space-based gravitational wave detections, the axion-like dark matter would alter the polarization state of the laser link between spacecrafts due to the birefringence effect. However, current designs of space-based laser interferometer are insensitive to variations in the polarization angle. Thus, the additional wave plates are employed to enable the response of the axion-induced birefring… ▽ More In the space-based gravitational wave detections, the axion-like dark matter would alter the polarization state of the laser link between spacecrafts due to the birefringence effect. However, current designs of space-based laser interferometer are insensitive to variations in the polarization angle. Thus, the additional wave plates are employed to enable the response of the axion-induced birefringence effect. We calculate and compare the sensitivities of different space-based detectors, accounting for three time-delay interferometry combinations, including Monitor, Beacon, and Relay. We find that the Monitor and Beacon combinations have better sensitivity in the high-frequency range, and the optimal sensitivity reaches $g_{aγ}\sim 10^{-13}\text{GeV}^{-1}$, while the Sagnac combination is superior in the low-frequency range. We also find that ASTROD-GW can cover the detection range of axion-like dark matter mass down to $10^{-20}\text{eV}$. △ Less

Submitted 19 November, 2025; originally announced November 2025.

Comments: 9 pages, 12 figures

Gravitational wave standard sirens from GWTC-3 combined with DESI DR2 and DESY5: A late-universe probe of the Hubble constant and dark energy

Authors: Ji-Yu Song, Guo-Hong Du, Tian-Nuo Li, Ling-Feng Wang, Jing-Zhao Qi, Jing-Fei Zhang, Xin Zhang

Abstract: Recently, the combination of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) data and the Planck cosmic microwave background (CMB) measurements has shown a $\sim$3$σ$ preference for a dynamical dark energy model with a phantom-crossing behavior. However, such a phantom-crossing dark energy evolution further exacerbates the already severe Hubbl… ▽ More Recently, the combination of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) data and the Planck cosmic microwave background (CMB) measurements has shown a $\sim$3$σ$ preference for a dynamical dark energy model with a phantom-crossing behavior. However, such a phantom-crossing dark energy evolution further exacerbates the already severe Hubble tension in the $Λ$CDM model. Moreover, there exists a $\sim2σ$ tension between the DESI DR2 BAO and CMB datasets. Therefore, it is essential to measure the Hubble constant and dark-energy equation-of-state (EoS) parameters using only late-universe observations. In this work, we investigate a novel late-universe data combination: gravitational-wave (GW) standard sirens, BAO, and Type Ia supernovae (SNe Ia). This combination provides a fully distance-ladder- and CMB-independent determination of the Hubble constant and the dark-energy EoS. Using 47 GW standard sirens from the third Gravitational-Wave Transient Catalog, the DESI DR2 BAO data, and DESY5 SNe Ia data, in the $w_0w_a$CDM model, we obtain $H_0=74.8^{+6.3}_{-8.9}$ km s$^{-1}$ Mpc$^{-1}$, $Ω_{\rm m}=0.320^{+0.015}_{-0.012}$, $w_0=-0.775^{+0.072}_{-0.074}$, and $w_a=-0.80\pm0.47$, indicating a mild phantom-crossing behavior within the $1σ$ credible interval with an $H_0$ value consistent with the distance ladder measurements. Our analysis demonstrates the power of GW standard sirens in breaking parameter degeneracies, and this novel data combination provides joint constraints on the Hubble constant and the dark-energy EoS parameters. △ Less

Submitted 14 November, 2025; originally announced November 2025.

Comments: 10 pages, 3 figures

Geometric Unification of Timelike Orbital Chaos and Phase Transitions in Black Holes

Authors: Shi-Hao Zhang, Zi-Yuan Li, Jing-Fei Zhang, Xin Zhang

Abstract: The deep connection between black hole thermodynamics and spacetime geometry remains a central focus of general relativity. While recent studies have revealed a precise correspondence for null orbits, given by $K = -λ^2$ between the Gaussian curvature $K$ and the Lyapunov exponent $λ$, its validity for timelike orbits had remained unknown. Our work introduces the massive particle surface (MPS) fra… ▽ More The deep connection between black hole thermodynamics and spacetime geometry remains a central focus of general relativity. While recent studies have revealed a precise correspondence for null orbits, given by $K = -λ^2$ between the Gaussian curvature $K$ and the Lyapunov exponent $λ$, its validity for timelike orbits had remained unknown. Our work introduces the massive particle surface (MPS) framework and constructs a new geometric quantity $\mathcal{G}$. We demonstrate that $\mathcal{G} \propto -λ^2$ on unstable timelike orbits, thus establishing the geometry-dynamics correspondence for massive particles. Crucially, near the first-order phase transition of a black hole, $\mathcal{G}$ displays synchronized multivalued behavior with the Lyapunov exponent $λ$ and yields a critical exponent $δ=1/2$. Our results demonstrate that spacetime geometry encodes thermodynamic information, opening a new pathway for studying black hole phase transitions from a geometric perspective. △ Less

Submitted 6 November, 2025; originally announced November 2025.

Comments: 7 pages, 1 figure

Conditional variational autoencoders for cosmological model discrimination and anomaly detection in cosmic microwave background power spectra

Authors: Tian-Yang Sun, Tian-Nuo Li, He Wang, Jing-Fei Zhang, Xin Zhang

Abstract: The cosmic microwave background power spectra are a primary window into the early universe. However, achieving interpretable, likelihood-compatible compression and fast inference under weak model assumptions remains challenging. We propose a parameter-conditioned variational autoencoder (CVAE) that aligns a data-driven latent representation with cosmological parameters while remaining compatible w… ▽ More The cosmic microwave background power spectra are a primary window into the early universe. However, achieving interpretable, likelihood-compatible compression and fast inference under weak model assumptions remains challenging. We propose a parameter-conditioned variational autoencoder (CVAE) that aligns a data-driven latent representation with cosmological parameters while remaining compatible with standard likelihood analyses. The model achieves high-fidelity compression of the $D_\ell^{TT}$, $D_\ell^{EE}$, and $D_\ell^{TE}$ spectra into just 5 latent dimensions, with reconstruction accuracy exceeding $99.9\%$ within Planck uncertainties. It reliably reconstructs spectra for beyond-$Λ$CDM scenarios, even under parameter extrapolation, and enables rapid inference, reducing the computation time from $\sim$40 hours to $\sim$2 minutes while maintaining posterior consistency. The learned latent space demonstrates a physically meaningful structure, capturing a distributed representation that mirrors known cosmological parameters and their degeneracies. Moreover, it supports highly effective unsupervised discrimination among cosmological models, achieving performance competitive with supervised approaches. Overall, this physics-informed CVAE enables anomaly detection beyond $Λ$CDM and points to physically meaningful directions for refinement. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 19 pages, 13 figures

Mapping Anisotropies in the Stochastic Gravitational-Wave Background with space detector networks

Authors: Zhi-Yuan Li, Zheng-Cheng Liang, Cong-mao Zhang, Jian-dong Zhang, Yi-Ming Hu

Abstract: Future space-based gravitational-wave detectors such as TianQin, LISA, and Taiji are expected to conduct joint observations. Such a multi-detector network will provide complementary viewing angles for the anisotropic stochastic gravitational-wave background (SGWB), thereby significantly enhancing the capability to reconstruct and localize its spatial distribution. In this paper, we have establishe… ▽ More Future space-based gravitational-wave detectors such as TianQin, LISA, and Taiji are expected to conduct joint observations. Such a multi-detector network will provide complementary viewing angles for the anisotropic stochastic gravitational-wave background (SGWB), thereby significantly enhancing the capability to reconstruct and localize its spatial distribution. In this paper, we have established the first dedicated data analysis pipeline for the anisotropic stochastic gravitational-wave background using a joint network of TianQin, LISA, and Taiji. Our analysis incorporates both Gaussian, stationary, and unpolarized point sources from diverse sky locations as well as a random sky map. We have performed full-sky map reconstruction in pixel space using maximum likelihood estimation to extract the angular distribution of the SGWB. The results demonstrate that, when considering the detector noise, the TianQin+LISA+Taiji detector network can reconstruct the angular power spectrum of the stochastic background up to a maximum multipole moment of $l = 14 $, which can provide valuable information for studies on the spatial distribution of galactic compact binaries and physical imprints from the early Universe. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Model-independent late-universe measurements of $H_0$ and $Ω_\mathrm{K}$ with the PAge-improved inverse distance ladder

Authors: Guo-Hong Du, Tian-Nuo Li, Jia-Le Ling, Yan-Hong Yao, Jing-Fei Zhang, Xin Zhang

Abstract: The standard $Λ{\rm CDM}$ model has encountered serious challenges and the $H_0$ tension has become more significant with increasingly precise cosmological observation. Meanwhile, inconsistencies in measurements of the curvature parameter $Ω_\mathrm{K}$ between different datasets also have emerged. In this work, we employ two global and cosmic age-based parameterizations, PAge and MAPAge, to perfo… ▽ More The standard $Λ{\rm CDM}$ model has encountered serious challenges and the $H_0$ tension has become more significant with increasingly precise cosmological observation. Meanwhile, inconsistencies in measurements of the curvature parameter $Ω_\mathrm{K}$ between different datasets also have emerged. In this work, we employ two global and cosmic age-based parameterizations, PAge and MAPAge, to perform model-independent measurements of the Hubble constant $H_0$ and $Ω_\mathrm{K}$ by utilizing the inverse distance ladder (IDL). To construct the PAge-improved IDL, we utilize the strong gravitational lensing (SGL), cosmic chronometers (CC), and gamma ray bursts (GRB) data to calibrate the latest DESI DR2 baryon acoustic oscillation data and DESY5 type Ia supernova data. Our analysis indicate that DESI+DESY5+SGL+CC+GRB gives $H_0=71.59\pm 0.94\,{\rm km}~{\rm s}^{-1}~{\rm Mpc}^{-1}$ in the MAPAge model, reducing the $H_0$ tension to the $1.0σ$ level. Extending to MAPAge$+Ω_{\rm K}$ model, we obtain $Ω_\mathrm{K}=0.001\pm 0.038$, which suggests that current late-time data are consistent with a flat universe. Finally, the Bayesian analysis indicates that the present late-universe data provide weak to moderate evidence in favor of PAge and MAPAge relative to $Λ{\rm CDM}$. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Comments: 12 pages, 2 figures

Synergy between CSST and third-generation gravitational-wave detectors: Inferring cosmological parameters using cross-correlation of dark sirens and galaxies

Authors: Ya-Nan Du, Ji-Yu Song, Yichao Li, Shang-Jie Jin, Ling-Feng Wang, Jing-Fei Zhang, Xin Zhang

Abstract: Gravitational-wave (GW) events are generally believed to originate in galaxies and can thus serve, like galaxies, as tracers of the universe's large-scale structure. In GW observations, waveform analysis provides direct measurements of luminosity distances; however, the redshifts of GW sources cannot be determined due to the mass-redshift degeneracy. By cross-correlating GW events with galaxies, o… ▽ More Gravitational-wave (GW) events are generally believed to originate in galaxies and can thus serve, like galaxies, as tracers of the universe's large-scale structure. In GW observations, waveform analysis provides direct measurements of luminosity distances; however, the redshifts of GW sources cannot be determined due to the mass-redshift degeneracy. By cross-correlating GW events with galaxies, one can establish a correspondence between luminosity distance and redshift shells, enabling cosmological inference. In this work, we explore the scientific potential of cross-correlating GW sources detected by third-generation (3G) ground-based GW detectors with the photometric redshift survey of the China Space Station Survey Telescope (CSST). We find that the constraint precisions of the Hubble constant and the matter density parameter can reach $1.04\%$ and $2.04\%$, respectively. The GW clustering bias parameters $A_{\rm GW}$ and $γ$ can be constrained to $1.52\%$ and $4.67\%$, respectively. These results highlight the significant potential of the synergy between CSST and 3G ground-based GW detectors in constraining cosmological models and probing GW source formation channels using cross-correlation of dark sirens and galaxies. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 15 pages, 7 figures

Subsystem fidelity in two-dimensional conformal field theories

Authors: Bin Sui, Yihao Wang, Jiaju Zhang

Abstract: We investigate the short-interval expansion of the subsystem fidelity in two-dimensional conformal field theories (2D CFTs) using the operator product expansion (OPE) of twist operators. We obtain universal contributions from general quasiprimary operators valid for arbitrary 2D CFTs, along with specific results in free massless boson and fermion theories. The analytical predictions demonstrate ex… ▽ More We investigate the short-interval expansion of the subsystem fidelity in two-dimensional conformal field theories (2D CFTs) using the operator product expansion (OPE) of twist operators. We obtain universal contributions from general quasiprimary operators valid for arbitrary 2D CFTs, along with specific results in free massless boson and fermion theories. The analytical predictions demonstrate excellent agreement with established analytical results in field theories and numerical calculations in integrable models. Furthermore, we extend the method to holographic CFTs, where subsystem fidelity serves to analyze the distinguishability of black hole microstates through the AdS/CFT correspondence. This work establishes a unified framework for quantifying quantum state distinguishability across various 2D CFTs, bridging quantum information techniques with applications in quantum gravity. △ Less

Submitted 20 October, 2025; originally announced October 2025.

Comments: 21 pages, 2 figures

From Stars to Waves: Non-deterministic Inference of Microlensed Gravitational Waves

Authors: Zhaoqi Su, Xikai Shan, Zhenwei Lyu, Junyao Zhang, Yebin Liu, Shude Mao, Huan Yang

Abstract: Strongly lensed gravitational waves may pass through the stellar field of a lensing galaxy with additional modulations (on both phase and amplitude) due to gravitational microlensing effect of stars/remnants near the line of sight. These microlensed waveforms depend on the mass and location of thousands or more most relevant stars, so that their deterministic reconstruction from the data is comput… ▽ More Strongly lensed gravitational waves may pass through the stellar field of a lensing galaxy with additional modulations (on both phase and amplitude) due to gravitational microlensing effect of stars/remnants near the line of sight. These microlensed waveforms depend on the mass and location of thousands or more most relevant stars, so that their deterministic reconstruction from the data is computationally prohibitive. We classify the detection and parameter estimation of such events as non-deterministic inference problem and propose a solution with the implementation of normalizing flows. As a first step, we show that $8\%$ of microlensed events can be detected with significance $\ge 3 σ$ in the third generation era, with the chosen microlensing parameters correlated with the density of the underlying stellar field. This approach opens the door to probing microlensing effects and the properties of the underlying stellar fields. A similar construction may also be applied to other non-deterministic inference problems, such as detecting post-merger gravitational waves from binary neutron star coalescence and signals from core-collapse supernovae. △ Less

Submitted 19 October, 2025; originally announced October 2025.

Comments: 19 pages, 11 figures, comments are welcome!

A Practical Framework for Estimating the Repetition Likelihood of Fast Radio Bursts from Spectral Morphology

Authors: Wan-Peng Sun, Yong-Kun Zhang, Ji-Guo Zhang, Xiaohui Liu, Yichao Li, Fu-Wen Zhang, Wan-Ting Hou, Jing-Fei Zhang, Xin Zhang

Abstract: The repeating behavior of fast radio bursts (FRBs) is regarded as a key clue to understanding their physical origin, yet reliably distinguishing repeaters from apparent non-repeaters with current observations remains challenging. Here we propose a physically interpretable and practically quantifiable classification framework based on spectral morphology. Using dimensionality reduction, clustering,… ▽ More The repeating behavior of fast radio bursts (FRBs) is regarded as a key clue to understanding their physical origin, yet reliably distinguishing repeaters from apparent non-repeaters with current observations remains challenging. Here we propose a physically interpretable and practically quantifiable classification framework based on spectral morphology. Using dimensionality reduction, clustering, and feature-importance analysis, we identify the spectral running $r$ and spectral index $γ$ as the most critical parameters for distinguishing repeaters from apparent non-repeaters in the CHIME/FRB sample. In the $γ$-$r$ space, repeaters preferentially occupy regions with steeper, narrower-band spectra, whereas non-repeaters cluster in flatter, broader-band regions, resulting in a clear density separation. We further construct an empirical probability map in the $γ$-$r$ space, showing a clear gradient of repetition likelihood, from $\sim 65\%$ in the high-repetition region to $\sim 5\%$ in the low-repetition region. Combining this with Gaussian Mixture Model posterior analysis, we identify several apparent non-repeaters with high inferred repetition probability, recommending them as priority targets for future monitoring. This framework provides a simple and generalizable tool for assessing repeatability in the CHIME/FRB sample and highlights the diagnostic power of spectral morphology in unveiling FRB origins. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Comments: 15 pages, 4 figures

One-loop Corrected Holographic Shear Viscosity to Entropy Density Ratio at Low Temperatures

Authors: Leopoldo A. Pando Zayas, Jingchao Zhang

Abstract: Near-extremal black holes are known to contain strong quantum fluctuations in their near-horizon near-AdS$_2$ throat region governed by an effective action that includes Schwarzian modes. These fluctuations lead to one-loop corrections in the gravitational path integral that are essential in understanding the thermodynamics of near-extremal black holes at low temperatures where they become more do… ▽ More Near-extremal black holes are known to contain strong quantum fluctuations in their near-horizon near-AdS$_2$ throat region governed by an effective action that includes Schwarzian modes. These fluctuations lead to one-loop corrections in the gravitational path integral that are essential in understanding the thermodynamics of near-extremal black holes at low temperatures where they become more dominant that the semi-classical answer. We explore the implications of these quantum fluctuations for near-extremal asymptotically AdS$_4$ black branes in the context of the AdS/CFT correspondence. We note that at one-loop level there is a coupling of the shear gravitational fluctuations to one of the would-be zero modes. This coupling affects the retarded Green's function in a way that leads to a low temperature violation of the shear viscosity to entropy density bound. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Comments: 19 pages, 2 figures

Report number: LITP-25-12

Alleviating the $H_0$ tension through new interacting dark energy model in light of DESI DR2

Authors: Yi-Min Zhang, Tian-Nuo Li, Guo-Hong Du, Sheng-Han Zhou, Li-Yang Gao, Jing-Fei Zhang, Xin Zhang

Abstract: The $H_0$ tension has become one of the most significant challenges in modern cosmology. The recent DESI DR2 data has shown a significant preference for dynamical dark energy, yet this has further exacerbated the $H_0$ tension. In this work, we explore the potential of new interacting dark energy models ($\widetildeΛ$CDM and $e\widetildeΛ$CDM) to alleviate the $H_0$ tension. We perform observation… ▽ More The $H_0$ tension has become one of the most significant challenges in modern cosmology. The recent DESI DR2 data has shown a significant preference for dynamical dark energy, yet this has further exacerbated the $H_0$ tension. In this work, we explore the potential of new interacting dark energy models ($\widetildeΛ$CDM and $e\widetildeΛ$CDM) to alleviate the $H_0$ tension. We perform observational constraints using the latest baryon acoustic oscillation data from DESI DR2, cosmic microwave background (CMB) data from Planck and Atacama Cosmology Telescop, and type Ia supernova data from DESY5 and PantheonPlus, as well as the SH0ES data. From our analysis, we observe the dynamical scale parameter of the cosmological constant, $δ_Λ = -0.410^{+0.140}_{-0.120}$, in the $e\widetildeΛ$CDM model using the CMB+DESI+SH0ES data, which deviates from $Λ$CDM at the $3.2σ$ level. Due to the anti-correlation between $δ_Λ$ and $H_0$, a negative $δ_Λ$ results in a higher inferred $H_0$. Consequently, we obtain $H_0 = 71.90 \pm 1.00~\mathrm{km\,s^{-1}\,Mpc^{-1}}$, reducing the $H_0$ tension to $0.8σ$. Even without SH0ES, the CMB+DESI data alone still alleviate the $H_0$ tension to $1.7σ$. Overall, the $e\widetildeΛ$CDM model not only deviates from the $Λ$CDM model but also demonstrates a significant capability to alleviate the $H_0$ tension. △ Less

Submitted 14 October, 2025; originally announced October 2025.

Comments: 12 pages, 4 figures

Updated constraints on interacting dark energy: A comprehensive analysis using multiple CMB probes, DESI DR2, and supernovae observations

Authors: Tian-Nuo Li, Guo-Hong Du, Yun-He Li, Yichao Li, Jia-Le Ling, Jing-Fei Zhang, Xin Zhang

Abstract: Recent DESI baryon acoustic oscillation (BAO) measurements, combined with Planck cosmic microwave background (CMB) data and DESY5 type Ia supernova (SN) data, indicate a significant deviation from $Λ$CDM, which seems to suggest that this deviation can be explained by an interaction between dark energy and dark matter. In this work, we perform a comprehensive analysis by utilizing the latest DESI D… ▽ More Recent DESI baryon acoustic oscillation (BAO) measurements, combined with Planck cosmic microwave background (CMB) data and DESY5 type Ia supernova (SN) data, indicate a significant deviation from $Λ$CDM, which seems to suggest that this deviation can be explained by an interaction between dark energy and dark matter. In this work, we perform a comprehensive analysis by utilizing the latest DESI DR2 BAO data in conjunction with CMB data from ACT, SPT, Planck, and WMAP, along with SN data from PantheonPlus and DESY5. We consider four interacting dark energy (IDE) models with different forms of the interaction term $Q$. Our analysis indicates that CMB experiments other than Planck enhance the evidence for an interaction in the IDE models with $Q \propto ρ_{\rm de}$. In particular, when using the SPT+DESI+DESY5 data, the IDE model with $Q = βH_0 ρ_{\rm de}$ gives $β= -0.4170 \pm 0.1220$, with a deviation from zero reaching $3.4σ$ level. When replacing DESY5 with PantheonPlus, this deviation weakens to $2.1σ$ level, but remains relatively significant. Furthermore, the Bayes factors of the IDE model with $Q = βH_0 ρ_{\rm de}$ are positive in all cases, providing a moderate-to-strong preference over $Λ$CDM. Overall, our comprehensive analysis clearly suggests that the IDE models with $Q \propto ρ_{\rm de}$ (especially, $Q = βH_0 ρ_{\rm de}$) provide strong evidence supporting the existence of interaction and are more preferred by the current cosmological data. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Comments: 17 pages, 3 figures

Black Hole Superradiance of Interacting Multi-Field

Authors: Zhi-Qing Zhu, Yun-Song Piao, Jun Zhang

Abstract: We investigate black hole superradiance evolution of the interacting multiple fields. We consider a model of two scalar fields interacting with a cubic coupling, and study the superradiant evolution of the cloud. We demonstrate that superradiance is typically suppressed when the superradiant field couples to another field, even with a very weak coupling strength. This implies that the constraints… ▽ More We investigate black hole superradiance evolution of the interacting multiple fields. We consider a model of two scalar fields interacting with a cubic coupling, and study the superradiant evolution of the cloud. We demonstrate that superradiance is typically suppressed when the superradiant field couples to another field, even with a very weak coupling strength. This implies that the constraints on dark particles derived from single-field analyses can be revised in the presence of interactions. Moreover, we find that the multi-field superradiant evolution and its corresponding observational signatures can be different across parameter spaces, which makes black hole superradiance an even more powerful probe of the dark sector in particle physics. △ Less

Submitted 13 September, 2025; originally announced September 2025.

Comments: 12 pages, 11 figures

Measuring neutrino masses with joint JWST and DESI DR2 data

Authors: Sheng-Han Zhou, Tian-Nuo Li, Guo-Hong Du, Jun-Qian Jiang, Jing-Fei Zhang, Xin Zhang

Abstract: Early JWST observations reveal an unexpectedly abundant population of high-redshift candidate massive galaxies at $z \gtrsim 7$, and recent DESI measurements show a preference for dynamical dark energy, which together present a significant challenge to the standard $Λ$CDM cosmology. In this work, we jointly analyze high-redshift galaxy data from JWST, baryon acoustic oscillations data from DESI DR… ▽ More Early JWST observations reveal an unexpectedly abundant population of high-redshift candidate massive galaxies at $z \gtrsim 7$, and recent DESI measurements show a preference for dynamical dark energy, which together present a significant challenge to the standard $Λ$CDM cosmology. In this work, we jointly analyze high-redshift galaxy data from JWST, baryon acoustic oscillations data from DESI DR2, and cosmic microwave background (CMB) data from Planck and ACT, measuring the total neutrino mass $\sum m_ν$. We consider three dark energy models ($Λ$CDM, $w$CDM, and $w_0w_a$CDM) and three mass hierarchies. Our results indicate that in the $w_0w_a$CDM model, adding JWST data to CMB+DESI tightens the upper limit of $\sum m_ν$ by about $5.8\%-10.2\%$, and we obtain $\sum m_ν < 0.167~\mathrm{eV}$ ($2σ$) in the normal hierarchy (NH) case. Furthermore, JWST also offers indicative lower limits on star formation efficiency parameter of $f_{*,10} \gtrsim 0.146-0.161$. Bayesian evidence weakly favors the $w_0w_a$CDM+$\sum m_ν$(NH) model relative to the $Λ$CDM+$\sum m_ν$(NH) model using CMB+DESI+JWST data. These results suggest that the joint analysis of high-redshift JWST data and low-redshift DESI data provides compelling constraints on neutrino mass and merits further investigation. △ Less

Submitted 17 December, 2025; v1 submitted 13 September, 2025; originally announced September 2025.

Comments: 11 pages, 3 figures

Journal ref: Physical Review D 112, 123532 (2025)

Gaussian curvature and Lyapunov exponent as probes of black hole phase transitions

Authors: Shi-Hao Zhang, Zi-Qiang Zhao, Zi-Yuan Li, Jing-Fei Zhang, Xin Zhang

Abstract: We study the Gaussian curvature of unstable null orbits. The Gaussian curvature exhibits multivaluedness near the phase transition point of a first-order phase transition. Numerical investigations of Reissner-Nordstrom Anti-de Sitter (RN-AdS), Hayward-AdS, and Hayward-Letelier-AdS black holes demonstrate that this geometric multivalued region coincides precisely with the spinodal region calculated… ▽ More We study the Gaussian curvature of unstable null orbits. The Gaussian curvature exhibits multivaluedness near the phase transition point of a first-order phase transition. Numerical investigations of Reissner-Nordstrom Anti-de Sitter (RN-AdS), Hayward-AdS, and Hayward-Letelier-AdS black holes demonstrate that this geometric multivalued region coincides precisely with the spinodal region calculated by black hole thermodynamics. Using the known relation $K=-λ^2$ linking orbital geometry to chaotic dynamics, we show that this geometric feature also satisfies the critical exponents predicted by mean-field theory, consistent with those derived from Lyapunov exponents. Our work demonstrates that Gaussian curvature can serve as an alternative effective tool to study the phase structure of black holes. △ Less

Submitted 5 September, 2025; originally announced September 2025.

Comments: 9 pages, 4 figures

Lightcurve Features of Magnetar-Powered Superluminous Supernovae with Gravitational-Wave Emission and High-Energy Leakage

Authors: Jinghao Zhang, Yacheng Kang, Jiahang Zhong, Hong-Bo Li, Liang-Duan Liu, Yun-Wei Yu, Lijing Shao

Abstract: Superluminous supernovae (SLSNe) are a distinct class of stellar explosions, exhibiting peak luminosities 10-100 times brighter than those of normal SNe. Their extreme luminosities cannot be explained by the radioactive decay of $^{56}\mathrm{Ni}$ and its daughter $^{56}\mathrm{Co}$ alone. Consequently, models invoking newly formed millisecond magnetars have been widely proposed, capable of supply… ▽ More Superluminous supernovae (SLSNe) are a distinct class of stellar explosions, exhibiting peak luminosities 10-100 times brighter than those of normal SNe. Their extreme luminosities cannot be explained by the radioactive decay of $^{56}\mathrm{Ni}$ and its daughter $^{56}\mathrm{Co}$ alone. Consequently, models invoking newly formed millisecond magnetars have been widely proposed, capable of supplying additional energy through magnetic dipole radiation. For these rapidly rotating magnetars, however, gravitational-wave (GW) emission may also contribute significantly to the spin-down, particularly during their early evolutionary stages. While high-energy photons initially remain trapped within the optically thick ejecta, they will eventually escape as the ejecta becomes transparent during the expansion, thereby influencing the late-time lightcurve. In this work, we adopt an analytical framework to systematically explore the combined effects of GW emission and high-energy leakage on the lightcurve of SLSNe. Compared to scenarios that neglect these processes, we find that for magnetars with initial spin periods of millisecond, the combined influence suppresses early-time luminosities but enhances late-time emission. We further investigate the effects of the neutron-star equation of state to the lightcurve, GW emission efficiency, ejecta mass, and other relevant quantities. Our results highlight the complex interplay between GW-driven spin-down and radiative transport in shaping the observable features of SLSNe, offering new insights into diagnosing the nature of their central engines. △ Less

Submitted 15 December, 2025; v1 submitted 26 August, 2025; originally announced August 2025.

Comments: 17 pages, 8 figures, accepted for publication in RAA

Common Envelope Evolution of Ultralight Boson Clouds

Authors: Ao Guo, Qi-Yan Zhang, Huan Yang, Jun Zhang

Abstract: Ultralight bosons can be excited around spinning black holes via black hole superradiance. These boson clouds may play an important role in the orbital evolution of binary black holes. In this work, we investigate the formation and evolution of common envelopes of ultralight boson clouds in comparable mass-ratio black hole binaries. We describe the cloud evolution using gravitational molecular eig… ▽ More Ultralight bosons can be excited around spinning black holes via black hole superradiance. These boson clouds may play an important role in the orbital evolution of binary black holes. In this work, we investigate the formation and evolution of common envelopes of ultralight boson clouds in comparable mass-ratio black hole binaries. We describe the cloud evolution using gravitational molecular eigenstates and analyze the possible level transitions during orbital decay, as well as the impact on orbital dynamics. We find that the cloud can generally lead to eccentricity growth. In particular, the eccentricity may vary significantly during level transition, leaving an eccentricity of ${\cal O}(0.1)$ within the detection band of ground-based gravitational wave detectors. △ Less

Submitted 26 August, 2025; originally announced August 2025.

Prospects for searching for sterile neutrinos in dynamical dark energy cosmologies using joint observations of gravitational waves and $γ$-ray bursts

Authors: Lu Feng, Tao Han, Jing-Fei Zhang, Xin Zhang

Abstract: In the era of third-generation (3G) gravitational-wave (GW) detectors, GW standard siren observations from binary neutron star mergers provide a powerful tool for probing the expansion history of the universe. Since sterile neutrinos can influence cosmic evolution by modifying the radiation content and suppressing structure formation, GW standard sirens offer promising prospects for constraining s… ▽ More In the era of third-generation (3G) gravitational-wave (GW) detectors, GW standard siren observations from binary neutron star mergers provide a powerful tool for probing the expansion history of the universe. Since sterile neutrinos can influence cosmic evolution by modifying the radiation content and suppressing structure formation, GW standard sirens offer promising prospects for constraining sterile neutrino properties within a cosmological framework. Building on this, we investigate the prospects for detecting sterile neutrinos in dynamical dark energy (DE) models using joint observations from 3G GW detectors and a future short gamma-ray burst detector, such as a THESEUS-like telescope. We consider three DE models: the $w$CDM, holographic DE (HDE), and Chevallier-Polarski-Linder (CPL) models. Our results show that the properties of DE can influence the constraints on sterile neutrino parameters. Moreover, the inclusion of GW data significantly improves constraints on both sterile neutrino parameters and other cosmological parameters across all three models, compared to the current limits derived from CMB+BAO+SN (CBS) observations. When GW data are included into the CBS dataset, a preference for $ΔN_{\rm eff} > 0$ emerges at approximately the $1σ$ level in the $w$CDM and CPL models, and reaches about $3σ$ in the HDE model. Moreover, the upper limits on $m_{ν,{\rm sterile}}^{\rm eff}$ are reduced by approximately 13%, 75%, and 3% in the $w$CDM, HDE, and CPL models, respectively. △ Less

Submitted 28 October, 2025; v1 submitted 23 July, 2025; originally announced July 2025.

Comments: 13 pages, 4 figures

Journal ref: Chinese Physics C 50 (2026) 015105

Cosmological Preference for a Positive Neutrino Mass at 2.7$σ$: A Joint Analysis of DESI DR2, DESY5, and DESY1 Data

Authors: Guo-Hong Du, Tian-Nuo Li, Peng-Ju Wu, Jing-Fei Zhang, Xin Zhang

Abstract: Neutrinos and dark energy (DE) have entered a new era of investigation, as the latest DESI baryon acoustic oscillation measurements tighten the constraints on the neutrino mass and suggest that DE may be dynamical rather than a cosmological constant. {In this work, we obtain a high-confidence measurement of the neutrino mass within a dynamical DE framework. A joint analysis of DESI DR2, cosmic mic… ▽ More Neutrinos and dark energy (DE) have entered a new era of investigation, as the latest DESI baryon acoustic oscillation measurements tighten the constraints on the neutrino mass and suggest that DE may be dynamical rather than a cosmological constant. {In this work, we obtain a high-confidence measurement of the neutrino mass within a dynamical DE framework. A joint analysis of DESI DR2, cosmic microwave background, DESY5 supernova, and DESY1 weak lensing data yields a total neutrino mass of $\sum m_ν= 0.098^{+0.016}_{-0.037}\,\mathrm{eV}$, indicating a measurement for a non-zero, positive neutrino mass at the $2.7σ$ level within the $w_0w_a$CDM framework. This high-confidence measurement is driven mainly by these factors: (i) the DESI's preference for a dynamical DE with its equation of state evolving from $w< -1$ at early times to $w> -1$ at late times, thus leading to a larger neutrino mass; (ii) treating $N_{\mathrm{eff}}$ as a free parameter together with the inclusion of weak lensing data, which likewise allows for an increased neutrino mass.} In future, even higher-confidence measurements of neutrino mass are expected with stronger preferences for dynamical DE in light of more complete DESI data releases. △ Less

Submitted 29 October, 2025; v1 submitted 22 July, 2025; originally announced July 2025.

Comments: 10 pages, 4 figures

Testing the cosmic distance duality relation with baryon acoustic oscillations and supernovae data

Authors: Tian-Nuo Li, Guo-Hong Du, Peng-Ju Wu, Jing-Zhao Qi, Jing-Fei Zhang, Xin Zhang

Abstract: One of the most fundamental relationships in modern cosmology is the cosmic distance duality relation (CDDR), which describes the relationship between the angular diameter distance ($D_{\rm A}$) and the luminosity distance ($D_{\rm L}$), and is expressed as: $η(z)=D_{\rm L}(z)(1+z)^{-2}/D_{\rm A}(z)=1$. In this work, we conduct a comprehensive test of the CDDR by combining baryon acoustic oscillat… ▽ More One of the most fundamental relationships in modern cosmology is the cosmic distance duality relation (CDDR), which describes the relationship between the angular diameter distance ($D_{\rm A}$) and the luminosity distance ($D_{\rm L}$), and is expressed as: $η(z)=D_{\rm L}(z)(1+z)^{-2}/D_{\rm A}(z)=1$. In this work, we conduct a comprehensive test of the CDDR by combining baryon acoustic oscillation (BAO) data from the SDSS and DESI surveys with type Ia supernova (SN) data from PantheonPlus and DESY5. We utilize an artificial neural network approach to match the SN and BAO data at the same redshift. To explore potential violations of the CDDR, we consider three different parameterizations: (i) $η(z)=1+η_0z$; (ii) $η(z)=1+η_0z/(1+z)$; (iii) $η(z)=1+η_0\ln(1+z)$. Our results indicate that the calibration of the SN absolute magnitude $M_{\rm B}$ plays a crucial role in testing potential deviations from the CDDR, as there exists a significant negative correlation between $η_0$ and $M_{\rm B}$. For PantheonPlus analysis, when $M_{\rm B}$ is treated as a free parameter, no evidence of CDDR violation is found. In contrast, fixing $M_{\rm B}$ to the $M_{\rm B}^{\rm D20}$ prior with $-19.230\pm0.040$ mag leads to a deviation at approximately the $2σ$ level, while fixing $M_{\rm B}$ to the $M_{\rm B}^{\rm B23}$ prior with $-19.396\pm0.016$ mag remains in agreement with the CDDR. Furthermore, overall analyses based on the SDSS+DESY5 and DESI+DESY5 data consistently show no evidence of the deviation from the CDDR. △ Less

Submitted 26 November, 2025; v1 submitted 18 July, 2025; originally announced July 2025.

Comments: 12 pages, 5 figures

Journal ref: Eur. Phys. J. C 85 (2025) 1354

Gravitational wave standard sirens: A brief review of cosmological parameter estimation

Authors: Shang-Jie Jin, Ji-Yu Song, Tian-Yang Sun, Si-Ren Xiao, He Wang, Ling-Feng Wang, Jing-Fei Zhang, Xin Zhang

Abstract: Gravitational wave (GW) observations are expected to serve as a powerful and independent probe of the expansion history of the universe. By providing direct and calibration-free measurements of luminosity distances through waveform analysis, GWs provide a fundamentally different and potentially more robust approach to measuring cosmic-scale distances compared to traditional electromagnetic observa… ▽ More Gravitational wave (GW) observations are expected to serve as a powerful and independent probe of the expansion history of the universe. By providing direct and calibration-free measurements of luminosity distances through waveform analysis, GWs provide a fundamentally different and potentially more robust approach to measuring cosmic-scale distances compared to traditional electromagnetic observations, which is known as the standard siren method. In this review, we present an overview of recent developments in GW standard siren cosmology, the latest observational results, and prospects for constraining cosmological parameters using future GW detections. We first introduce standard sirens based on how redshift information is obtained and outline the Bayesian framework used in cosmological parameter estimation. We then review the measurements on the Hubble constant from the LIGO-Virgo-KAGRA network and present the potential role of future standard siren observations in cosmological parameter estimations. A central focus of this review is the unique ability of GW observations to break cosmological parameter degeneracies inherent in the EM observations. Since the cosmological parameter degeneracy directions of GW and EM observations are quite different (roughly orthogonal in some cases), their combination can significantly improve constraints on cosmological parameters. This complementarity is expected to become one of the most critical advantages for GW standard siren cosmology. Looking forward, we highlight the importance of combining GW standard sirens with other emerging late-universe cosmological probes such as fast radio bursts, 21 cm intensity mapping, and strong gravitational lensing to forge a precise cosmological probe for exploring the late universe. Finally, we introduce the challenges and the role of machine learning in future standard siren analysis. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Comments: 36 pages, 20 figures

Prospects for joint multiband detection of intermediate-mass black holes by LGWA and the Einstein Telescope

Authors: Yue-Yan Dong, Ji-Yu Song, Jing-Fei Zhang, Xin Zhang

Abstract: Gravitational-wave (GW) detection offers a novel approach to exploring intermediate-mass black holes (IMBHs). The GW signals from IMBH mergers mainly fall in the decihertz frequency band. The lunar-based GW detector, the Lunar Gravitational-Wave Antenna (LGWA), exhibits high sensitivity in this band, making it particularly well-suited for detecting IMBHs. However, for lower-mass IMBHs, the late in… ▽ More Gravitational-wave (GW) detection offers a novel approach to exploring intermediate-mass black holes (IMBHs). The GW signals from IMBH mergers mainly fall in the decihertz frequency band. The lunar-based GW detector, the Lunar Gravitational-Wave Antenna (LGWA), exhibits high sensitivity in this band, making it particularly well-suited for detecting IMBHs. However, for lower-mass IMBHs, the late inspiral and merger signals enter the sensitive frequency range of ground-based GW detectors. In this work, we aim to explore how multi-band observations with LGWA and the third-generation ground-based GW detector, the Einstein Telescope (ET), can contribute to detecting the population of IMBHs. We consider three population distribution cases of IMBHs, including two population models based on astrophysical motivations and a uniform distribution, and compute the signal-to-noise ratios for LGWA, ET, and their combination to directly compare their capabilities in detecting IMBH mergers. Our results suggest that LGWA possesses strong detection capability for high-mass IMBH mergers. At redshift $z = 1$, LGWA's detection rate for IMBH binaries with primary masses above $5 \times 10^4~M_\odot$ is largely insensitive to orbital inclination and mass ratio. In contrast, ET is more suited for detecting IMBH binaries with primary masses below $10^3~M_\odot$. The multi-band observation of LGWA and ET possesses strong detection capabilities across the full IMBH mass spectrum. Furthermore, we find that the multi-band detection can significantly and effectively recover the IMBH population distributions. In summary, we conclude that the multi-band observations of LGWA and ET will provide powerful detection capabilities for IMBHs and are expected to significantly enhance our understanding of this important yet still poorly observed class of black holes. △ Less

Submitted 14 December, 2025; v1 submitted 14 July, 2025; originally announced July 2025.

Comments: 21 pages, 8 figures; accepted for publication in JCAP

Exploring non-cold dark matter in a scenario of dynamical dark energy with DESI DR2 data

Authors: Tian-Nuo Li, Peng-Ju Wu, Guo-Hong Du, Yan-Hong Yao, Jing-Fei Zhang, Xin Zhang

Abstract: Recent observations of DESI hint that dark matter (DM) may not be cold but have a non-zero equation of state (EoS) parameter, and that dark energy (DE) may not be a cosmological constant. In this work, we explore the possibility of a non-zero DM EoS parameter within the framework of dynamical DE. We perform analysis by using the latest baryon acoustic oscillation (BAO) data from DESI DR2, the cosm… ▽ More Recent observations of DESI hint that dark matter (DM) may not be cold but have a non-zero equation of state (EoS) parameter, and that dark energy (DE) may not be a cosmological constant. In this work, we explore the possibility of a non-zero DM EoS parameter within the framework of dynamical DE. We perform analysis by using the latest baryon acoustic oscillation (BAO) data from DESI DR2, the cosmic microwave background (CMB) data from Planck, and the type Ia supernova (SN) data from DESY5 and PantheonPlus. When using the combination of CMB, BAO, and SN data, our results indicate a preference for a non-zero DM EoS parameter at the $2.8σ$ and $3.3σ$ level within the content of a constant DE EoS. In contrast, for a time-evolving DE EoS parameterized by $w_0$ and $w_a$, this preference decreases to $0.8σ$ and $1.1σ$. Furthermore, allowing a non-zero DM EoS yields best-fit values of $w_0$ and $w_a$ that exhibit smaller deviations from the $Λ$CDM expectations, and Bayesian evidence analysis shows a comparable preference for this model relative to $Λ$CDM. The overall results of this work indicate that a non-zero DM EoS parameter warrants further exploration and investigation. △ Less

Submitted 10 July, 2025; originally announced July 2025.

Comments: 8 pages, 5 figures

Journal ref: Physics of the Dark Universe 50 (2025) 102068

Cosmic baryon census with fast radio bursts and gravitational waves

Authors: Ji-Guo Zhang, Ji-Yu Song, Ze-Wei Zhao, Wan-Peng Sun, Jing-Fei Zhang, Xin Zhang

Abstract: The cosmic baryon density fraction ($Ω_{\rm b}$) is intrinsically correlated with the Hubble constant ($H_0$) through the critical density of the Universe. In the context of the decade-long $H_0$ tension, the significant discrepancy between early- and late-Universe measurements of $H_0$ implies that fixing its value or imposing an external prior could bias the baryon census. To address this concer… ▽ More The cosmic baryon density fraction ($Ω_{\rm b}$) is intrinsically correlated with the Hubble constant ($H_0$) through the critical density of the Universe. In the context of the decade-long $H_0$ tension, the significant discrepancy between early- and late-Universe measurements of $H_0$ implies that fixing its value or imposing an external prior could bias the baryon census. To address this concern, we construct a late-Universe probe framework that unifies fast radio bursts (FRBs) and gravitational-wave (GW) standard sirens, which can respectively resolve the missing baryon problem and the $H_0$ tension through their dispersion measures and absolute luminosity distances. By combining $104$ localized FRBs with $47$ GW events, we obtain an $H_0$-free measurement of $Ω_{\rm b}=0.0488\pm0.0064$ ($1σ$), in concordance with early-Universe observations of CMB + BBN. Although the current precision ($\sim 13\%$) is limited by sample size, the growing detections of both FRBs and GWs will make their synergy a powerful probe of low-redshift cosmology. △ Less

Submitted 2 December, 2025; v1 submitted 9 July, 2025; originally announced July 2025.

Comments: 14 pages, 4 figures

Phase transitions in a holographic superfluid model with non-linear terms beyond the probe limit

Authors: Zi-Qiang Zhao, Zhang-Yu Nie, Jing-Fei Zhang, Xin Zhang

Abstract: We study the holographic s-wave superfluid model with 4th and 6th power self-interaction terms $λ|ψ|^4$ and $τ|ψ|^6$ with considering the full back-reaction of the matter fields on the metric in the 3+1 dimensional bulk. The self-interaction terms are good at controlling the condensate to realize various phase transitions, such as the zeroth-order, first-order, and second-order phase transitions w… ▽ More We study the holographic s-wave superfluid model with 4th and 6th power self-interaction terms $λ|ψ|^4$ and $τ|ψ|^6$ with considering the full back-reaction of the matter fields on the metric in the 3+1 dimensional bulk. The self-interaction terms are good at controlling the condensate to realize various phase transitions, such as the zeroth-order, first-order, and second-order phase transitions within the single condensate s-wave superfluid model. Therefore, in this work, we are able to investigate the influence of the back-reaction strength on the various phase transitions, including the zeroth and first order phase transitions. In addition, we confirm that the influence of the 4th and 6th power terms on the superfluid phase transition in the case of finite back-reaction are qualitative the same as in the probe limit, thus present universality. We also plot the special value $λ_s$ of the parameter $λ$ at different back-reaction strength, below which the condensate grows to an opposite direction and is important in controlling the order of the superfluid phase transitions. Comparing the influence of the back-reaction parameter and that of the higher-order nonlinear coefficients, we see that the back-reaction strength brings in both the effective couplings similar to the 4th power and 6th power terms. △ Less

Submitted 3 October, 2025; v1 submitted 12 June, 2025; originally announced June 2025.

Comments: 9 pages, 10 figures; published in EPJC

Journal ref: Eur. Phys. J. C 85 (2025) 9, 1064

Revisiting the phenomenologically emergent dark energy model: is non-zero equation of state of dark matter favored by DESI DR2?

Authors: Tian-Nuo Li, Yi-Min Zhang, Yan-Hong Yao, Peng-Ju Wu, Jing-Fei Zhang, Xin Zhang

Abstract: The nature of dark matter remains one of the most fundamental and unresolved questions in modern cosmology. In most cosmological models, dark matter is typically modeled as pressureless dust with an equation of state (EoS) parameter $w_{\rm dm} = 0$. However, there is no fundamental theoretical reason to exclude the possibility of a non-zero dark matter EoS parameter. In this work, we explore the… ▽ More The nature of dark matter remains one of the most fundamental and unresolved questions in modern cosmology. In most cosmological models, dark matter is typically modeled as pressureless dust with an equation of state (EoS) parameter $w_{\rm dm} = 0$. However, there is no fundamental theoretical reason to exclude the possibility of a non-zero dark matter EoS parameter. In this work, we explore the possibility of a non-zero dark matter EoS within the phenomenologically emergent dark energy (PEDE) model, given its simplicity and proven ability to alleviate the Hubble tension. We perform observational constraints by using the latest baryon acoustic oscillation data from DESI DR2, the cosmic microwave background (CMB) data from Planck, and the type Ia supernova data from DESY5 and PantheonPlus. From our analysis, we observe that a negative dark matter EoS parameter is preferred in all scenarios. Specifically, the CMB+DESI+DESY5 data yields $w_{\mathrm{dm}} = -0.00093 \pm 0.00032$, deviating from zero at approximately the $3σ$ level. However, this deviation is likely driven by unidentified systematics or inconsistencies in the DESY5 data, with the deviation decreasing to $2σ$ when using PantheonPlus data. Meanwhile, a negative $w_{\rm dm}$ would increase the Hubble tension due to the positive degeneracy between $w_{\rm dm}$ and $H_0$. Furthermore, Bayesian evidence suggests that the $Λ$CDM model is strongly preferred over the PEDE+$w_{\rm dm}$ model. These analyses illustrate that it is not possible to both support a non-cold dark matter component within the PEDE model and alleviate the Hubble tension simultaneously. △ Less

Submitted 18 December, 2025; v1 submitted 11 June, 2025; originally announced June 2025.

Comments: 23 pages, 6 figures

Journal ref: JCAP 12 (2025) 048

Can we live in a baby universe formed by a delayed first-order phase transition?

Authors: Qing-Hong Cao, Masanori Tanaka, Jun-Chen Wang, Ke-Pan Xie, Jing-Jun Zhang

Abstract: We examine the idea that our universe began as a baby universe and show that this is feasible in a $U(1)_{B-L}$ extension of the Standard Model with the classically conformal principle. The framework is consistent with current cosmological data and predicts a heavy neutral gauge boson, which could be detected at colliders. We examine the idea that our universe began as a baby universe and show that this is feasible in a $U(1)_{B-L}$ extension of the Standard Model with the classically conformal principle. The framework is consistent with current cosmological data and predicts a heavy neutral gauge boson, which could be detected at colliders. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 5 pages, 2 figures

Report number: CPTNP-2025-014

Model-independent cosmological inference after the DESI DR2 data with improved inverse distance ladder

Authors: Jia-Le Ling, Guo-Hong Du, Tian-Nuo Li, Jing-Fei Zhang, Shao-Jiang Wang, Xin Zhang

Abstract: Recently, the baryon acoustic oscillations (BAO) measurements from the DESI survey have suggested hints of dynamical dark energy, challenging the standard $Λ$CDM model. In this work, we adopt an improved inverse distance ladder approach based on the latest cosmological data to provide a model-independent perspective, employing a global parametrization based on cosmic age (PAge). Our analysis incor… ▽ More Recently, the baryon acoustic oscillations (BAO) measurements from the DESI survey have suggested hints of dynamical dark energy, challenging the standard $Λ$CDM model. In this work, we adopt an improved inverse distance ladder approach based on the latest cosmological data to provide a model-independent perspective, employing a global parametrization based on cosmic age (PAge). Our analysis incorporates DESI DR2 BAO measurements, cosmic chronometer (CC) data, and type Ia supernovae (SNe) observations from either the DESY5 or PantheonPlus datasets. For the DESY5+DESI DR2+CC datasets, we obtain $H_0 = 67.91 \pm 2.33~\mathrm{km~s^{-1}~Mpc^{-1}}$. This value is consistent with the Planck 2018 result, while shows $2.0 σ$ tension with the SH0ES measurement. Furthermore, by mapping specific cosmological models into PAge approximation parameter space $(p_{\mathrm{age}}, η)$, our model-independent analysis reveals a notable deviation from the $Λ\mathrm{CDM}$ model, as indicated by the DESY5 and DESI DR2 datasets. Finally, DESY5+DESI DR2+CC datasets provide nearly decisive evidence favoring the PAge model over the standard $Λ\mathrm{CDM}$ model. These findings highlight the need for further investigation into the expansion history to better understand the deviations from the $Λ\mathrm{CDM}$ model. △ Less

Submitted 10 October, 2025; v1 submitted 28 May, 2025; originally announced May 2025.

Comments: 16 pages, 6 figures; accepted for publication in Physical Review D

Journal ref: Physical Review D 112, 083528 (2025)

Parameter inference of microlensed gravitational waves using neural spline flows

Authors: Zheng Qin, Tian-Yang Sun, Bo-Yuan Li, Jing-Fei Zhang, Xiao Guo, Xin Zhang

Abstract: When gravitational waves (GWs) propagate near massive objects, they undergo gravitational lensing that imprints lens model dependent modulations on the waveform. This effect provides a powerful tool for cosmological and astrophysical studies. However, conventional Bayesian parameter inference methods for GWs are computationally expensive, especially for lensed events with additional lens parameter… ▽ More When gravitational waves (GWs) propagate near massive objects, they undergo gravitational lensing that imprints lens model dependent modulations on the waveform. This effect provides a powerful tool for cosmological and astrophysical studies. However, conventional Bayesian parameter inference methods for GWs are computationally expensive, especially for lensed events with additional lens parameters, necessitating more efficient approaches. In this work, we explore the use of neural spline flows (NSFs) for posterior inference of microlensed GWs, and successfully apply NSFs to the inference of 11-dimensional lens parameters. Our results demonstrate that compared with traditional methods like Bilby dynesty that rely on Bayesian inference, the NSF network we built not only achieves inference accuracy comparable to traditional methods for the main parameters, but also can reduce the inference time from approximately 3 days to 0.8 s on average. Additionally, the network exhibits strong generalization for the spin parameters of GW sources. It is anticipated to become a powerful tool for future low-latency searches for lensed GW signals. △ Less

Submitted 16 July, 2025; v1 submitted 27 May, 2025; originally announced May 2025.

Comments: 11 pages, 6 figures

Towards Realistic Detection Pipelines of Taiji: New Challenges in Data Analysis and High-Fidelity Simulations of Space-Borne Gravitational Wave Antenna

Authors: Minghui Du, Pengcheng Wang, Ziren Luo, Wen-Biao Han, Xin Zhang, Xian Chen, Zhoujian Cao, Xilong Fan, He Wang, Xiaodong Peng, Li-E Qiang, Ke An, Yidi Fan, Jiafeng Zhang, Liang-Gui Zhu, Ping Shen, Qianyun Yun, Xiao-Bo Zou, Ye Jiang, Tianyu Zhao, Yong Yuan, Xiaotong Wei, Yuxiang Xu, Bo Liang, Peng Xu , et al. (1 additional authors not shown)

Abstract: Taiji, a Chinese space-based gravitational wave detection project, aims to explore the millihertz gravitational wave universe with unprecedented sensitivity, targeting astrophysical and cosmological sources including Galactic binaries, massive black hole binaries, extreme mass-ratio inspirals, and stochastic gravitational wave backgrounds, etc. These observations are expected to provide transforma… ▽ More Taiji, a Chinese space-based gravitational wave detection project, aims to explore the millihertz gravitational wave universe with unprecedented sensitivity, targeting astrophysical and cosmological sources including Galactic binaries, massive black hole binaries, extreme mass-ratio inspirals, and stochastic gravitational wave backgrounds, etc. These observations are expected to provide transformative insights into astrophysics, cosmology, and fundamental physics. However, Taiji's data analysis faces unique challenges distinct from ground-based detectors like LIGO-Virgo-KAGRA, such as the overlap of numerous signals, extended data durations, more rigorous accuracy requirements for the waveform templates, non-negligible subdominant waveform complexities, incompletely characterized noise spectra, non-stationary noises, and various data anomalies. This paper presents the second round of Taiji Data Challenge, a collection of simulation datasets designed as a shared platform for resolving these critical data analysis problems. The current platform distinguishes from previous works by the systematic integration of orbital dynamics based on the full drag-free and attitude control simulation, extended noise sources, more sophisticated and overlapping gravitational wave signals, second-generation time-delay interferometry and the coupling effect of time-varying armlengths, etc. Concurrently released is the open-source toolkit Triangle (available at https://github.com/TriangleDataCenter), which offers the capabilities for customized simulation of signals, noises and other instrumental effects. By taking a step further towards realistic detection, Taiji Data Challenge II and Triangle altogether serve as a new testbed, supporting the development of Taiji's global analysis and end-to-end pipelines, and ultimately bridging the gaps between observation and scientific objectives. △ Less

Submitted 23 May, 2025; v1 submitted 22 May, 2025; originally announced May 2025.

Multi-messenger standard-siren cosmology for third-generation gravitational-wave detectors: Considering observations of gamma-ray bursts and kilonovae

Authors: Tao Han, Jing-Fei Zhang, Xin Zhang

Abstract: In the third-generation (3G) gravitational-wave (GW) detector era, GW multi-messenger observations for binary neutron star merger events can exert great impacts on exploring the cosmic expansion history. Extending the previous work, we explore the potential of 3G GW standard siren observations in cosmological parameter estimation by considering their associated electromagnetic (EM) counterparts, i… ▽ More In the third-generation (3G) gravitational-wave (GW) detector era, GW multi-messenger observations for binary neutron star merger events can exert great impacts on exploring the cosmic expansion history. Extending the previous work, we explore the potential of 3G GW standard siren observations in cosmological parameter estimation by considering their associated electromagnetic (EM) counterparts, including $γ$-ray burst (GRB) coincidence observations by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor and GW-triggered target-of-opportunity observations of kilonovae by different optical survey projects. During an assumed 10-year observation, we predict that the number of detectable GW-kilonova events is $\sim 4900$ with redshifts below $\sim 0.4$ under GW network and Large Synoptic Survey Telescope in the $i$ band, which is three times more than that of GW-GRB detections. For the cosmological analysis, we find that with the inclusion of GW-kilonova detections, the constraints on cosmological parameters from GW-EM detections are significantly improved compared to those from GW-GRB detections. In particular, GW-EM detections can tightly constrain the Hubble constant with a precision ranging from $0.076\%$ to $0.034\%$. Moreover, GW multi-messenger observations could effectively break the cosmological parameter degeneracies generated by the mainstream EM observations, CMB+BAO+SN (CBS). The combination of CBS and GW-EM can tightly constrain the equation of state parameters of dark energy $w$ in the $w$CDM model and $w_0$ in the $w_0w_a$CDM model with precisions of $0.72\%$ and $0.99\%$, respectively, meeting the standard of precision cosmology. In conclusion, GW multi-messenger observations could play a crucial role in helping solve the Hubble tension and probing the fundamental nature of dark energy. △ Less

Submitted 24 April, 2025; originally announced April 2025.

Comments: 21 pages, 14 figures

Bayesian model selection of Primordial Black Holes and Dressed Primordial Black Holes with lensed Gravitational Waves

Authors: Xin-yi Lin, Zhengxiang Li, Jian-dong Zhang

Abstract: If particle dark matter (DM) and primordial black holes (PBHs) coexist, PBHs will be surrounded by particle DM, forming celestial objects known as dressed PBHs (dPBHs). These structures suggest a scenario in which PBHs and DM can exist simultaneously. However, in the high-frequency regime, the gravitational lensing effect of bare PBHs is similar to that of dPBHs. Ground-based gravitational wave (G… ▽ More If particle dark matter (DM) and primordial black holes (PBHs) coexist, PBHs will be surrounded by particle DM, forming celestial objects known as dressed PBHs (dPBHs). These structures suggest a scenario in which PBHs and DM can exist simultaneously. However, in the high-frequency regime, the gravitational lensing effect of bare PBHs is similar to that of dPBHs. Ground-based gravitational wave (GW) detectors are particularly sensitive to high-frequency GW signals. In this regime, the lensing effect of a point-mass lens with a mass in the range of $10^{-1} \sim 10^2 M_{\odot}$ becomes significant. In this work, we incorporate dPBH models with GW observations and employ Bayesian inference techniques to distinguish PBHs from dPBHs. Using the third-generation ground-based GW detectors, Einstein Telescope (ET) and Cosmic Explorer (CE), as examples, we demonstrate that these detectors can effectively differentiate the lensing effects of dPBHs from those of PBHs across a broad frequency range. Furthermore, we find that with a larger black hole (BH) mass inside the surrounding particle DM, ET and CE can distinguish these two lensed models with even greater precision. △ Less

Submitted 21 April, 2025; originally announced April 2025.

Toward Second-Order Self-Force for Eccentric Extreme-Mass Ratio Inspirals in Schwarzschild Spacetime

Authors: Yi-Xiang Wei, Xian-Long Zhu, Jian-dong Zhang, Jianwei Mei

Abstract: An Extreme Mass Ratio Inspiral (EMRI), which corresponds to a small compact object inspirals around a massive black hole in the center of a galaxy, is one of the most important sources for future space-borne gravitational-wave (GW) detectors such as TianQin and LISA. By analyzing the emitted GW signals, we can probe the theory of gravity and the nature of black holes in the strong field region. To… ▽ More An Extreme Mass Ratio Inspiral (EMRI), which corresponds to a small compact object inspirals around a massive black hole in the center of a galaxy, is one of the most important sources for future space-borne gravitational-wave (GW) detectors such as TianQin and LISA. By analyzing the emitted GW signals, we can probe the theory of gravity and the nature of black holes in the strong field region. To achieve these objectives, the second-order self-force effect should be considered in the waveform modeling. Up to now, the waveform of EMRIs including the second-order self-force effect is only achieved for the circular orbit on Schwarzschild background. In this work, we generalized the calculation of the second-order self-force to the eccentric orbits on Schwarzschild spacetime. We calculated the puncture field, and give the form of two-timescale expansion for the field equations. The corresponding numerical calculation and programming can be performed based on these results. △ Less

Submitted 24 September, 2025; v1 submitted 13 April, 2025; originally announced April 2025.

Comments: 18 pages, 3 figures, 1 table, matches the published version

Journal ref: PhysRevD.112.064048 (2025)

Perturbative distinguishability of black hole microstates from AdS/CFT correspondence

Authors: Jiaju Zhang

Abstract: We establish direct evidence for the perturbative distinguishability between black hole microstates and thermal states using the AdS/CFT correspondence. In two-dimensional holographic conformal field theories, we obtain the subsystem fidelity and quantum Jensen-Shannon divergence, both of which provide rigorous lower and upper bounds for subsystem trace distance. This result demonstrates that pert… ▽ More We establish direct evidence for the perturbative distinguishability between black hole microstates and thermal states using the AdS/CFT correspondence. In two-dimensional holographic conformal field theories, we obtain the subsystem fidelity and quantum Jensen-Shannon divergence, both of which provide rigorous lower and upper bounds for subsystem trace distance. This result demonstrates that perturbative quantum gravity corrections break semiclassical indistinguishability, thereby supporting the recovery of information even from a small amount of the Hawking radiation. △ Less

Submitted 7 December, 2025; v1 submitted 11 April, 2025; originally announced April 2025.

Comments: 6 pages, no figure, published version

Journal ref: Phys. Rev. D 112 (2025) 12, L121901

Characterized behaviors of black hole thermodynamics in the supercritical region

Authors: Zi-Qiang Zhao, Zhang-Yu Nie, Jing-Fei Zhang, Xin Zhang

Abstract: The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure. This study is devoted to the analysis of characteristic lines and crossover behaviors within the supercritical region. By making use of the free energy, we introduce three key thermodynamic quantities: scaled vari… ▽ More The comprehension of universal thermodynamic behaviors in the supercritical region is crucial for examining the characteristics of black hole systems under high temperature and pressure. This study is devoted to the analysis of characteristic lines and crossover behaviors within the supercritical region. By making use of the free energy, we introduce three key thermodynamic quantities: scaled variance, skewness, and kurtosis. Our results demonstrate that the Widom line, associated with the maximal scaled variance, can effectively differentiate between small and large black hole-like subphases, each displaying distinct thermodynamic behaviors within the supercritical region. Furthermore, by utilizing quasinormal modes, we identify the Frenkel line, offering a dynamic perspective to distinguish between small and large black hole-like subphases. These contribute to a deeper comprehension of black hole subphases in the supercritical region, thus illuminating new facets of black hole thermodynamics. △ Less

Submitted 14 October, 2025; v1 submitted 7 April, 2025; originally announced April 2025.

Comments: 5 pages, 3 figures

Journal ref: Chinese Physics Letters 42, 101102 (2025)

Gravitational Waves from Superradiant Cloud Level Transition

Authors: Si-Tong Peng, Jun Zhang

Abstract: Ultralight boson clouds can form around black holes in binaries through superradiance, and undergo resonant level transitions at certain orbit frequencies. In this work, we investigate the gravitational waves emitted by the clouds during resonant level transitions, and forecast their detectability with future gravitational wave observations. We find that, for scalar fields of mass around… ▽ More Ultralight boson clouds can form around black holes in binaries through superradiance, and undergo resonant level transitions at certain orbit frequencies. In this work, we investigate the gravitational waves emitted by the clouds during resonant level transitions, and forecast their detectability with future gravitational wave observations. We find that, for scalar fields of mass around $10^{-12}$ eV, clouds in stellar mass black hole binaries can radiate gravitational waves around $0.1$ Hz during hyperfine level transition, that can be detected with future gravitational wave detectors such as DECIGO and BBO, providing a potential way of searching for ultralight boson fields. We also consider the clouds in intermediate mass black hole binaries, which can emit milli-Hz gravitational waves during hyperfine level transition. The resulting gravitational waves, however, can be hardly detected with LISA-like detectors. △ Less

Submitted 11 April, 2025; v1 submitted 1 April, 2025; originally announced April 2025.

Comments: 9 pages, 4 figures, figures updated, new results added, typos corrected

A search for sterile neutrinos in interacting dark energy models using DESI baryon acoustic oscillations and DES supernovae data

Authors: Lu Feng, Tian-Nuo Li, Guo-Hong Du, Jing-Fei Zhang, Xin Zhang

Abstract: Sterile neutrinos can influence the evolution of the universe, and thus cosmological observations can be used to search for sterile neutrinos. In this study, we utilized the latest baryon acoustic oscillations data from DESI, combined with the cosmic microwave background data from Planck and the five-year supernova data from DES, to constrain the interacting dark energy (IDE) models involving both… ▽ More Sterile neutrinos can influence the evolution of the universe, and thus cosmological observations can be used to search for sterile neutrinos. In this study, we utilized the latest baryon acoustic oscillations data from DESI, combined with the cosmic microwave background data from Planck and the five-year supernova data from DES, to constrain the interacting dark energy (IDE) models involving both cases of massless and massive sterile neutrinos. We consider four typical forms of the interaction term $Q=βH ρ_{\rm de}$, $Q=βH ρ_{\rm c}$, $Q=βH_{0} ρ_{\rm de}$, and $Q=βH_{0} ρ_{\rm c}$, respectively. Our analysis indicates that the current data provide only a hint of the existence of massless sterile neutrinos (as dark radiation) at about the $1σ$ level. In contrast, no evidence supports the existence of massive sterile neutrinos. Furthermore, in IDE models, the inclusion of (massless/massive) sterile neutrinos has a negligible impact on the constraint of the coupling parameter $β$. The IDE model of $Q=βH ρ_{\rm c}$ with sterile neutrinos does not favor an interaction. However, the other three IDE models with sterile neutrinos support an interaction in which dark energy decays into dark matter. △ Less

Submitted 13 March, 2025; originally announced March 2025.

Comments: 8 pages, 3 figures

Journal ref: Physics of the Dark Universe 48 (2025) 101935

Model-independent $H_0$ within FLRW: Joint constraints from GWTC-3 standard sirens and strong lensing time delays

Authors: Ji-Yu Song, Jing-Zhao Qi, Jing-Fei Zhang, Xin Zhang

Abstract: We use 47 gravitational-wave (GW) standard sirens from the third Gravitational-Wave Transient Catalog to calibrate distances in the strong gravitational lensing (SGL) system RXJ1131-1231 and constrain the Hubble constant ($H_0$) via the distance sum rule, without assuming a specific cosmological model. For $Ω_K = 0$, we obtain $H_0 = 73.22^{+5.95}_{-5.43}$ ${\rm km}~{\rm s}^{-1}~{\rm Mpc}^{-1}$ an… ▽ More We use 47 gravitational-wave (GW) standard sirens from the third Gravitational-Wave Transient Catalog to calibrate distances in the strong gravitational lensing (SGL) system RXJ1131-1231 and constrain the Hubble constant ($H_0$) via the distance sum rule, without assuming a specific cosmological model. For $Ω_K = 0$, we obtain $H_0 = 73.22^{+5.95}_{-5.43}$ ${\rm km}~{\rm s}^{-1}~{\rm Mpc}^{-1}$ and $H_0 = 70.40^{+8.03}_{-5.60}$ ${\rm km}~{\rm s}^{-1}~{\rm Mpc}^{-1}$ by breaking the mass-sheet transform using lens galaxy's mass models and stellar kinematics, respectively. Allowing $Ω_K$ to vary increases the central value of $H_0$ and reduces its precision. We find that GW dark sirens have significant potential for calibrating SGL systems, due to their relatively higher redshifts. By combining 42 binary black holes and RXJ1131-1231, we obtain an $H_0$ constraint with a precision approximately $40\%$ better than the measurement from GW170817 using the Hubble law. This suggests that high-precision, model-independent $H_0$ measurements can be achieved with this method as the redshift range of GW dark sirens expands, even without the need for GW bright sirens. △ Less

Submitted 20 May, 2025; v1 submitted 13 March, 2025; originally announced March 2025.

Comments: 8 pages, 2 figures; accepted for publication in The Astrophysical Journal Letters

Journal ref: Astrophys. J. Lett. 985 (2025) 2, L44

Fundamental Physics and Cosmology with TianQin

Authors: Jun Luo, Haipeng An, Ligong Bian, Rong-Gen Cai, Zhoujian Cao, Wenbiao Han, Jianhua He, Martin A. Hendry, Bin Hu, Yi-Ming Hu, Fa Peng Huang, Shun-Jia Huang, Sang Pyo Kim, En-Kun Li, Yu-Xiao Liu, Vadim Milyukov, Shi Pi, Konstantin Postnov, Misao Sasaki, Cheng-Gang Shao, Lijing Shao, Changfu Shi, Shuo Sun, Anzhong Wang, Pan-Pan Wang , et al. (10 additional authors not shown)

Abstract: The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the futu… ▽ More The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the future? These are the basic questions that press for answers. The space-based gravitational wave detector TianQin will tune in to gravitational waves in the millihertz frequency range ($10^{-4} \sim 1$ Hz, to be specific), opening a new gravitational wave spectrum window to explore many of the previously hidden sectors of the universe. TianQin will discover many astrophysical systems, populating the universe at different redshifts: some will be of new types that have never been detected before, some will have very high signal-to-noise ratios, and some will have very high parameter estimation precision. The plethora of information collected will bring us to new fronts on which to search for the breaking points of general relativity, the possible violation of established physical laws, the signature of possible new gravitational physics and new fundamental fields, and to improve our knowledge on the expansion history of the universe. In this white paper, we highlight the advances that TianQin can bring to fundamental physics and cosmology. △ Less

Submitted 27 February, 2025; originally announced February 2025.

Comments: 113 pages

Progress of the TianQin project

Authors: Jun Luo, Shaojun Bai, Yan-Zheng Bai, Lin Cai, Hao Dang, Qijia Dong, Hui-Zong Duan, Yuanbo Du, Lei Fan, Xinju Fu, Yong Gao, Xingyu Gou, Changlei Guo, Wei Hong, Bin Hu, Heran Hu, Ming Hu, Yi-Ming Hu, Fa Peng Huang, Defeng Gu, Xin Ji, Yuan-Ze Jiang, En-Kun Li, Hongyin Li, Ming Li , et al. (76 additional authors not shown)

Abstract: TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will… ▽ More TianQin is a future space-based gravitational wave observatory targeting the frequency window of $10^{-4}$ Hz $\sim 1$ Hz. A large variety of gravitational wave sources are expected in this frequency band, including the merger of massive black hole binaries, the inspiral of extreme/intermediate mass ratio systems, stellar-mass black hole binaries, Galactic compact binaries, and so on. TianQin will consist of three Earth orbiting satellites on nearly identical orbits with orbital radii of about $10^5$ km. The satellites will form a normal triangle constellation whose plane is nearly perpendicular to the ecliptic plane. The TianQin project has been progressing smoothly following the ``0123" technology roadmap. In step ``0", the TianQin laser ranging station has been constructed and it has successfully ranged to all the five retro-reflectors on the Moon. In step ``1", the drag-free control technology has been tested and demonstrated using the TianQin-1 satellite. In step ``2", the inter-satellite laser interferometry technology will be tested using the pair of TianQin-2 satellites. The TianQin-2 mission has been officially approved and the satellites will be launched around 2026. In step ``3", i.e., the TianQin-3 mission, three identical satellites will be launched around 2035 to form the space-based gravitational wave detector, TianQin, and to start gravitational wave detection in space. △ Less

Submitted 16 February, 2025; originally announced February 2025.

Comments: 45 pages, 3 figures